For many applications of resins (solid polymers), effective resistance to flame ignition is required. In order to increase the flame retardant properties of various and meet an industry or government standard of flame retardancy for specific polymers, flame retardant additives (organic and inorganic) are commonly admixed therewith and/or chemically bonded thereto in the case of polymer-reactive flame retardants. Organic flame retardants such as halogenated flame retardants, specifically brominated flame retardants, and phosphorus-containing flame retardants are considered to be effective for this purpose.
Inorganic flame retardants are another class of known flame retardant. Usually higher loading of inorganic flame retardants such as aluminum hydroxide, titania, carbon black, zinc oxide, antimony trioxide, etc., are required than that of halogenated flame retardants to achieve the same level of flame retardancy. However, high loading of inorganic flame retardants can negatively affect the optical and mechanical properties of the base polymer. In the case of flame retardant resin compositions containing organophosphorus flame retardant compounds such as triphenyl phosphate (TPP), combustion may tend to produce relatively high levels of smoke.
In many applications such as helmets, bullet proof glass, etc., optical transparency of the molding resin, e.g., polycarbonate at various service temperatures including low temperatures, is an important functional requirement. However, the addition of inorganic flame retardant(s) often reduces the transparency of the host resin.
Polydimethylsiloxane is a popular class of flame retardant for polycarbonate as the combustion products are less toxic than that of halogenated flame retardants. Due to the difference in compatibility between the polycarbonate and the silicone, the incorporation of silicone flame retardant in polycarbonate can reduce the optical transparency and increase haze of the polycarbonate-silicone flame retardant blend.
Therefore, there is a need for an improved flame retardant resin composition which produces less toxic combustion products than those produced by conventional or otherwise known flame retardant resin compositions, e.g., those containing organic halogen- or phosphorus-based flame retardant compounds, while providing improved optical and/or mechanical properties compared with those of known flame retardant resin composition containing inorganic flame retardant compounds.